diff --git a/aider/coders/base_coder.py b/aider/coders/base_coder.py
index 86d45b718..e6ba5d192 100755
--- a/aider/coders/base_coder.py
+++ b/aider/coders/base_coder.py
@@ -1624,7 +1624,10 @@ class Coder:
         return cur + new
 
     def get_rel_fname(self, fname):
-        return os.path.relpath(fname, self.root)
+        try:
+            return os.path.relpath(fname, self.root)
+        except ValueError:
+            return fname
 
     def get_inchat_relative_files(self):
         files = [self.get_rel_fname(fname) for fname in self.abs_fnames]
diff --git a/aider/linter.py b/aider/linter.py
index b24b6d7d4..86e5e8f76 100644
--- a/aider/linter.py
+++ b/aider/linter.py
@@ -52,7 +52,10 @@ class Linter:
 
     def get_rel_fname(self, fname):
         if self.root:
-            return os.path.relpath(fname, self.root)
+            try:
+                return os.path.relpath(fname, self.root)
+            except ValueError:
+                return fname
         else:
             return fname